Audio processing integrated circuit chips, such as codec (coder/decoder) chips are commonly used in consumer electronic devices, such as desktop computers, notebook computers, tablets and smart phones. For example, desktop and notebook computers typically include a codec chip that is used to process audio signals transmitted to and received from external audio devices, such as microphones and headphones. Such a codec chip may be configured to interface with a digital bus connected to the computer's CPU chip set, and includes signal processing circuitry, such as analog to digital converters (ADCs), digital-to-analog converters (DACs), filters, mixers and multiplexers. The bus communications of such codec chips typically conform to a standardized protocol, such that described by the Intel® High Definition Audio Specification.
Portable devices, such as notebook computers, are typically constrained by battery capacity. Thus, it is generally desirable for the electronic circuitry used in a portable device to conserve energy. In codec chips, power conservation may be achieved by selective activation of power supplies to circuits such as DACs and ADCs, and by reducing bias voltages provided to output circuits, such as port amplifier circuits that are used to drive external headphones and speakers.
CPU chipsets typically include the capability to generate audio signals that may be used for diagnostic and other purposes. For example, desktop and notebook chip sets typically generate a PC beep signal that may be used to signal boot up, reset, fault or other operating system conditions. This PC beep signal may be an analog signal, a 1-bit digital audio signal or a pulse-width modulated (PWM) signal (analog or digital derived). Conventional codec chips may route such a PC beep signal to one or more port amplifiers or other output circuits of the codec chip. Accordingly, even when the codec chip is in a low power mode, it maintains one or more port output circuits in an enabled state so that the PC beep can be transmitted to speakers, headphones or other devices coupled to the codec chip.